- Rickettsiae: small pathogens in family Ricket-tsiaceae (Table 26-1)
- Gram-negative coccobacilli/short bacilli; obligate localization/persistence within eukaryotic cells
- Transmitted to humans by arthropods: tick, mite, flea, louse; mammalian reservoirs; humans are incidental hosts
- Infections characterized by:
- Exposure to vectors or animal reservoirs, travel to or residence in endemic locations
- Clinical findings: fever, exanthem or tâche noire (black spot or stain) (coin-like lesion with central eschar and red halo at site of vector-feeding bite site) (Table 26-1), vasculitis, hepatosplenomegaly
- Thrombocytopenia, leukopenia, elevated aminotransferase, hyponatremia
- Diagnosis: confirmed by paired serum samples after convalescence or demonstration of microbes
- Dermatopathology: microbes multiply in endothelial cells of small blood vessels and produce vasculitis with necrosis and thrombosis; disseminated intravascular coagulation (DIC) and vascular occlusion may occur
- Doxycycline is drug of choice
Table 26-1 Classification of Groups of Rickettsial Infections and Clinical Features |Favorite Table|Download (.pdf)
Table 26-1 Classification of Groups of Rickettsial Infections and Clinical Features
Groups of Rickettsial Infections
Tick- and gamasid mite–borne spotted fever group (SFG)
Exanthem is a major clinical and diagnostic feature
Tâche noire, maculopapular rash
Tâche noire, papulovesicular rash
Flea- and louse-borne typhus group rickettsial disease
Trunkal maculopapular rash
Epidemic louse-borne typhus
Generalized maculopapular rash, sparing the face, palms, and soles, possibly becoming petechial andsconfluent
Endemic flea-borne murine typhus
Maculopapular rash occurring on the extremities and trunk, sparing the face, palms, and soles, in 13% of patients
Chigger-borne scrub typhus
Eschar at site of chigger feeding (< 50% of cases); maculopapular rash may occur, but seldom observed
Rash in ≤5% at onset
Rickettsiae can cause life-threatening infections. Order of decreasing case-fatality rate: R. rickettsii [Rocky Mountain spotted fever (RMSF)]; R. prowazekii (epidemic louse-borne typhus); Orientia tsutsugamushi (scrub typhus); R. conorii [Mediterranean spotted fever (MSF)]; R. typhi (endemic murine typhus); in rare cases, other spotted fever group organisms.
ICD-9:066.1 • ICD-10: A77
Table 26-2 Classification of Tick-Borne Rickettsial Spotted Fevers |Favorite Table|Download (.pdf)
Table 26-2 Classification of Tick-Borne Rickettsial Spotted Fevers
Rocky Mountain spotted fever
Western hemisphere (Americas)
Rocky Mountain spotted fever
Mediterranean countries, Africa, Southeast Asia, India
Siberia, Mongolia, northern China
Siberian tick typhus
Astralian tick typhus
Oriental spotted fever
African tick bite fever
Rocky Mountain Spotted Fever
ICD-9: O82.0 • ICD-10: A77
- Etiology: R. rickettsii
- Vector: various ticks
- Geography: occurs throughout Western Hemisphere (Americas)
- Most severe of rickettsial infections
- Classic triad: fever, rash, history of tick bite (not common)
- Clinical findings: sudden onset of fever, severe headache, myalgia, characteristic acral exanthem spreading centripetally
- Course: associated with significant morbidity and mortality rates
- Synonyms: black measles, tick ...
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